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Lisa's bucket does not have a hole in it and weighs 21 kg when full of water.

After she pours out half the water from the bucket it weighs 12 kg.

What is the weight of the empty bucket?

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.

*This problem is taken from the UKMT Mathematical Challenges.**View the archive of all weekly problems grouped by curriculum topic*